At the moment the compressor only accepts ASCII (upto 256) characters even though Javascript supports UTF-16 characters in its strings. For now, unless you can specify your required characters in the dict parameter, you should base64-encode your input prior to compression if it contains non-latin script. By base64 encoding you'll also be able to pass in a more limited dictionary character list and thereby gain greater compression ratios.

There are also dictionary optimisations which can be made to decrease the amount of memory used by the dictionary though speed will be impacted as a result.